Structural testing
50 DECEMBER 2019 \\ AEROSPACETESTINGINTERNATIONAL.COM
SPACE TRIALS
Professor Kazuya Yoshida
from the Department of
Aerospace Engineering at
Tohoku University in Japan
believes that there are two
main approaches suitable for
testing robots destined for
use in space:
“One is a common
procedure for all space
flight systems, including
mechanical vibration tests
using shaker tables that can
emulate the mechanical and
acoustic-induced vibrations
from the rocket engines
during the lift-off, thermalvacuum
tests and tests for
radioactive tolerance using
a radioactive source such as
Cobalt 60 isotope.
“The other type is more
specific. For in-orbit
operations, a microgravity
environment has a substantial
influence on the motion
dynamics and control,
therefore its testing is
important, but it is not easy to
emulate the microgravity on
the ground.
“One idea is to use an
air floating testbed on a 2D
plane, and the other one is to
use a free-fall capsule or an
airplane in a parabolic flight.
“As for lunar/planetary
rovers, locomotion and
navigation testing in analog
sites – outdoor field tests, are
crucial. To develop a space
robotics system, we need to
consider all these things.”
systems. He explains. Testing on robots heading for zero
gravity environments is usually done using air-floating
testbeds, in a free-fall capsule dropped from a high
altitude or in an aircraft during a parabolic flight.
There are also vacuum effects on heat transfer to
consider. In the atmosphere, heat can be transferred by
conduction, radiation and convection. “In the vacuum
environment, convection is not available, so the thermal
design of the systems becomes difficult. The vacuum
also makes the lubrication of the joints and sliding
elements difficult.”
TESTING CHALLENGES
Hoyt believes that there is a lot of work to be done to
ensure manufacturing technologies meet the
requirements of long-duration manned missions. “For
applications on the ISS and proposed Lunar Gateway, the
iSM tools will need to meet very strict requirements for
astronaut safety, fit within the power, mass, thermal, and
volume constraints of the ISS Express Rack payload
systems and achieve the verifiable precision and build
quality needed for mission-critical parts,” he says.
For metallic parts, heat-treatment is often needed to
achieve the desired material characteristics. However,
ways of performing heat treatments in a microgravity
environment in a manner that is safe for astronauts
remains a large technology gap.
For manufacturing large structures for spacecraft
systems, the development of robotic manufacturing and
assembly systems and their autonomous control
software – especially those that needed to diagnose and
resolve anomalous behavior as they operate, pose a
significant challenge.
“Previous and ongoing activities have highlighted the
technology gaps, which include validation of the
developed processes in the relevant environment,” says
Makaya. “They are being identified to help define future
activities on the topic.” \\
4 // Archinaut One will be
launched in 2022 to test its
robotic additive space
construction technology
environmental testing, which can include
vibration, shock and thermal testing.
“These laboratory tests can evaluate
the impacts of one or two elements of the
space environment, but to test them all
together we really need to fly
experiments in space,” he explains.
Most aspects of system functionality
can be tested individually on the ground
except those dominated by gravity effects.
The effects of gravity on manufacturing
processes can be studied in microgravity
testing, either on parabolic flight aircraft
or suborbital rockets such as Blue Origin’s
New Shepherd.
ZERO TO HERO
There are several ways zero-gravity can
affect manufacturing processes. “Where
thermal behavior is important, the lack of
convection in a microgravity environment
can dramatically change the temperature
at which components operate,” says Hoyt.
“That is difficult to recreate on the
ground but can be approximated with
insulation or operation in vacuum.”
The forces on mechanical parts can
also be much lower without gravity.
Gravity offloading rigs that use
suspension lines to support robotic arms
or other mechanisms can be used to
approximate that effect.
Micro-gravity has effects on motion
dynamics and control. Professor Kazuya
Yoshida from the Department of
Aerospace Engineering at Tohoku
University specializes in space robotics
and the dynamics and controls of space
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